School of Physics - Research Publications

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    Control of Neuronal Survival and Development Using Conductive Diamond
    Falahatdoost, S ; Prawer, YDJ ; Peng, D ; Chambers, A ; Zhan, H ; Pope, L ; Stacey, A ; Ahnood, A ; Al Hashem, HN ; De Leon, SE ; Garrett, DJ ; Fox, K ; Clark, MB ; Ibbotson, MR ; Prawer, S ; Tong, W (AMER CHEMICAL SOC, 2024-01-17)
    This study demonstrates the control of neuronal survival and development using nitrogen-doped ultrananocrystalline diamond (N-UNCD). We highlight the role of N-UNCD in regulating neuronal activity via near-infrared illumination, demonstrating the generation of stable photocurrents that enhance neuronal survival and neurite outgrowth and foster a more active, synchronized neuronal network. Whole transcriptome RNA sequencing reveals that diamond substrates improve cellular-substrate interaction by upregulating extracellular matrix and gap junction-related genes. Our findings underscore the potential of conductive diamond as a robust and biocompatible platform for noninvasive and effective neural tissue engineering.
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    Atomically Thin Synaptic Devices for Optoelectronic Neuromorphic Vision
    Ahmed, T ; Jannat, A ; Krishnamurthi, V ; Aung, T ; Mazumder, A ; Zavabeti, A ; Syed, N ; Daeneke, T ; Ou, JZ ; AI-Hourani, A ; Walia, S (Wiley, 2023)
    Imaging sensors with inbuilt processing capability are expected to form the backbone of low-latency and highly energy efficient artificial vision systems. A range of emerging atomically thin materials provide opportunities to exploit their electrical and optical properties for human vision and brain inspired functions. This work reports atomically thin nanosheets of β-In2S3 which exhibit inherent persistent photoconductivity (PPC) under ultraviolet and visible wavelengths. This PPC effect enables β-In2S3-based optoelectronic devices to optically mimic the dynamics of biological synapses. Based on the material characterizations, the PPC effect is attributed to the intrinsic defects in the synthesized β-In2S3 nanosheet. Furthermore, the feasibility of adopting these atomically thin synaptic devices for optoelectronic neuromorphic hardware is demonstrated by implementing a convolutional neural network for image classification. As such, the demonstrated atomically thin nanosheets and optoelectronic synaptic devices provide a platform for scaling up complex vision-sensory neural networks, which can find many promising applications for multispectral imaging and neuromorphic computation.
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    Near-infrared characterization of ultra-diffuse galaxies in Abell 2744 by JWST/NIRISS imaging
    Ikeda, R ; Morishita, T ; Tsukui, T ; Vulcani, B ; Trenti, M ; Metha, B ; Acebron, A ; Bergamini, P ; Grillo, C ; Iono, D ; Mercurio, A ; Rosati, P ; Vanzella, E (Oxford University Press (OUP), 2023-08-01)
    ABSTRACT We present a search and characterization of ultra-diffuse galaxies (UDGs) in the Frontier Fields cluster Abell 2744 at $z$ = 0.308. We use JWST/NIRISS F200W observations, acquired as part of the GLASS-JWST Early Release Science programme, aiming to characterize morphologies of cluster UDGs and their diffuse stellar components. A total number of 22 UDGs are identified by our selection criteria using morphological parameters, down to stellar mass of ∼107 M⊙. The selected UDGs are systematically larger in effective radius in F200W than in Hubble Space Telescope (HST)/ACS F814W images, which implies that some of them would not have been identified as UDGs when selected at rest-frame optical wavelengths. In fact, we find that about one-third of the UDGs were not previously identified based on the F814W data. We observe a flat distribution of the UDGs in the stellar mass–size plane, similar to what is found for cluster quiescent galaxies at comparable mass. Our pilot study using the new JWST F200W filter showcases the efficiency of searching UDGs at cosmological distances, with 1/30 of the exposure time of the previous deep observing campaign with HST. Further studies with JWST focusing on spatially resolved properties of individual sources will provide insight into their origin.
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    Instant-in-Air Liquid Metal Printed Ultrathin Tin Oxide for High-Performance Ammonia Sensors
    Nguyen, CK ; Taylor, PD ; Zavabeti, A ; Alluhaybi, H ; Almalki, S ; Guo, X ; Irfan, M ; Al Kobaisi, M ; Ippolito, SJ ; Spencer, MJS ; Balendhran, S ; Roberts, A ; Daeneke, T ; Crozier, KB ; Sabri, Y ; Syed, N (Wiley, 2024)
    Liquid metal-based printing techniques are emerging as an exemplary platform for harvesting non-layered 2D materials with a thickness down to a few nanometres, leading to an ultra-large surface-area-to-volume ratio that is ideal for sensing applications. In this work, the synthesis of 2D tin dioxide (SnO2) by exfoliating the surface oxide of molten tin is reported which highlights the enhanced sensing capability of the obtained materials to ammonia (NH3) gas is reported. It is demonstrated that amperometric gas sensors based on liquid metal-derived 2D SnO2 nanosheets can achieve excellent NH3 sensing performance at low temperature (150 °C) with and without UV light assistance. Detection over a wide range of NH3 concentrations (5–500 ppm) is observed, revealing a limit of detection at the parts per billion (ppb) level. The 2D SnO2 nanosheets also feature excellent cross-interference performance toward different organic and inorganic gas species, showcasing a high selectivity. Further, ab initio DFT calculations reveal the NH3 adsorption mechanism is dominated by chemisorption with a charge transfer into 2D SnO2 nanosheets. In addition, a proof of concept for prototype flexible ammonia sensors is demonstrated by depositing 2D SnO2 on a polyimide substrate, signifying the high potential of employing liquid metal printed SnO2 for realizing wearable gas sensors.
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    Characterising the Pelletron beam at the University of Melbourne
    Steinberg, AF ; Yap, JSL ; Norman, HXQ ; Appleby, RB ; Sheehy, SL (Elsevier, 2024-02-01)
    The Pelletron at the University of Melbourne is a DC particle accelerator that has been used for materials analysis and ion implantation since its installation in the 1970s. Today, it is primarily used to produce proton and helium beams up to 3.5 MeV and 1.5 MeV respectively, for three beamlines with a range of different experiments. The beam stability and fundamental beam parameters such as the transverse phase space distribution and emittance have not been previously investigated in detail. We have performed systematic measurements to determine the beam current variation, finding persistent fluctuations: our study determined that internal wire scanners used for monitoring the beam profile contribute to a periodic current drop. We also found that large terminal voltage oscillations reduce the average current. In addition, the phase space has been measured using a custom-built slit-grid apparatus. We found that the Courant–Snyder (Twiss) parameters are a function of the operational characteristics of the Pelletron, with the emittance more than doubling between measurements. To parametrise the beam despite the fluctuations, we introduce a ‘minimum bounding ellipse’ described by a set of Courant–Snyder parameters that is representative of the beam characteristics for all the measurements: for our data, this has β= 8.2(5) m, α=-5.2(3), and an emittance of 0.34(3) mm mrad. These parameters will enable future beamline design in Melbourne, and give an indication for the requirements at other Pelletron facilities. Our characterisation techniques can provide a low-cost method to probe beam parameters for improvements in the operation and efficiency of similar DC accelerators, allowing for more accurate measurements and reduced data acquisition times.
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    Early Results from GLASS-JWST. XVIII. A First Morphological Atlas of the 1 < z < 5 Universe in the Rest-frame Optical
    Jacobs, C ; Glazebrook, K ; Calabro, A ; Treu, T ; Nannayakkara, T ; Jones, T ; Merlin, E ; Abraham, R ; Stevens, ARH ; Vulcani, B ; Yang, L ; Bonchi, A ; Boyett, K ; Bradac, M ; Castellano, M ; Fontana, A ; Marchesini, D ; Malkan, M ; Mason, C ; Morishita, T ; Paris, D ; Santini, P ; Trenti, M ; Wang, X (IOP Publishing Ltd, 2023-05-01)
    Abstract We present a rest-frame optical morphological analysis of galaxies observed with the NIRCam imager on the James Webb Space Telescope (JWST) as part of the GLASS-JWST Early Release Science program. We select 388 sources at redshifts 0.8 < z < 5.4 and use the seven 0.9–5 μm NIRCam filters to generate rest-frame gri composite color images, and conduct visual morphological classification. Compared to Hubble Space Telescope (HST)–based work we find a higher incidence of disks and bulges than expected at z > 1.5, revealed by rest-frame optical imaging. We detect 123 clear disks (58 at z > 1.5) of which 76 have bulges. No evolution of bulge fraction with redshift is evident: 61% at z < 2 (N = 110) versus 60% at z ≥ 2 (N = 13). A stellar mass dependence is evident, with bulges visible in 80% of all disk galaxies with mass >109.5 M ⊙ (N = 41) but only 52% at M < 109.5 M ⊙ (N = 82). We supplement visual morphologies with nonparametric measurements of Gini and asymmetry coefficients in the rest-frame i band. Our sources are more asymmetric than local galaxies, with slightly higher Gini values. When compared to high-z rest-frame ultraviolet measurements with HST, JWST shows more regular morphological types such as disks, bulges, and spiral arms at z > 1.5, with smoother (i.e., lower Gini) and more symmetrical light distributions.
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    Early Results from GLASS-JWST. XV. Properties of the Faintest Red Sources in the NIRCAM Deep Fields
    Glazebrook, K ; Nanayakkara, T ; Jacobs, C ; Leethochawalit, N ; Calabro, A ; Bonchi, A ; Castellano, M ; Fontana, A ; Mason, C ; Merlin, E ; Morishita, T ; Paris, D ; Trenti, M ; Treu, T ; Santini, P ; Wang, X ; Boyett, K ; Bradac, M ; Brammer, G ; Jones, T ; Marchesini, D ; Nonino, M ; Vulcani, B (IOP Publishing Ltd, 2023-04-01)
    Abstract We present a first look at the reddest 2–5 μm sources found in deep images from the GLASS Early Release Science program. We undertake a general search, i.e., not looking for any particular spectral signatures, for sources detected only in bands redder than is reachable with the Hubble Space Telescope, and which would likely not have been identified in pre-JWST surveys. We search for sources down to AB ∼27 (corresponding to >10σ detection threshold) in any of the F200W to F444W filters, with a >1 magnitude excess relative to F090W to F150W bands. Fainter than F444W >25 we find 56 such sources of which 37 have reasonably constrained spectral energy distributions to which we can fit photometric redshifts. We find the majority of this population (∼65%) as 2 < z < 6 star-forming low-attenuation galaxies that are faint at rest-frame ultraviolet-optical wavelengths, have stellar masses 108.5–109.5 M ⊙, and have observed fluxes at >2 μm boosted by a combination of the Balmer break and emission lines. The typical implied rest equivalent widths are ∼200 Å with some extreme objects up to ∼1000 Å. This is in contrast with brighter magnitudes where the red sources tend to be z < 3 quiescent galaxies and dusty star-forming objects. Our general selection criteria for red sources allow us to independently identify other phenomena as diverse as extremely low-mass (∼108 M ⊙) quiescent galaxies at z < 1, recovering recently identified z > 11 galaxies and a very cool brown dwarf.
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    Measuring the Vortex-Nucleus Pinning Force from Pulsar Glitch Rates
    Melatos, A ; Millhouse, M (IOP Publishing Ltd, 2023-05-01)
    Abstract Superfluid vortex avalanches are one plausible cause of pulsar glitch activity. If they occur according to a state-dependent Poisson process, the measured long-term glitch rate is determined by the spin-down rate of the stellar crust, Ω ̇ c , and two phenomenological parameters quantifying the vortex−nucleus pinning force: a crust−superfluid angular velocity lag threshold, X cr, and a reference unpinning rate, λ 0. A Bayesian analysis of 541 glitches in 177 pulsars, with N g ≥ 1 events per pulsar, yields X cr = 0.15 − 0.04 + 0.09 rad s − 1 , λ ref = 7.6 − 2.6 + 3.7 × 10 − 8 s − 1 , and a = − 0.27 − 0.03 + 0.04 assuming the phenomenological rate law λ 0 = λ ref[τ/(1 yr)] a , where τ denotes the characteristic spin-down age. The results are broadly similar, whether one includes or excludes quasiperiodic glitch activity, giant glitches, or pulsars with N g = 0, up to uncertainties about the completeness of the sample and the total observation time per pulsar. The X cr and λ 0 estimates are consistent with first-principles calculations based on nuclear theory, e.g., in the semiclassical local density approximation.
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    JWST PEARLS. Prime Extragalactic Areas for Reionization and Lensing Science: Project Overview and First Results
    Windhorst, RA ; Cohen, SH ; Jansen, RA ; Summers, J ; Tompkins, S ; Conselice, CJ ; Driver, SP ; Yan, H ; Coe, D ; Frye, B ; Grogin, N ; Koekemoer, A ; Marshall, MA ; O'Brien, R ; Pirzkal, N ; Robotham, A ; Ryan, RE ; Willmer, CNA ; Carleton, T ; Diego, JM ; Keel, WC ; Porto, P ; Redshaw, C ; Scheller, S ; Wilkins, SM ; Willner, SP ; Zitrin, A ; Adams, NJ ; Austin, D ; Arendt, RG ; Beacom, JF ; Bhatawdekar, RA ; Bradley, LD ; Broadhurst, T ; Cheng, C ; Civano, F ; Dai, L ; Dole, H ; D'Silva, JCJ ; Duncan, KJ ; Fazio, GG ; Ferrami, G ; Ferreira, L ; Finkelstein, SL ; Furtak, LJ ; Gim, HB ; Griffiths, A ; Hammel, HB ; Harrington, KC ; Hathi, NP ; Holwerda, BW ; Honor, R ; Huang, J-S ; Hyun, M ; Im, M ; Joshi, BA ; Kamieneski, PS ; Kelly, P ; Larson, RL ; Li, J ; Lim, J ; Ma, Z ; Maksym, P ; Manzoni, G ; Meena, AK ; Milam, SN ; Nonino, M ; Pascale, M ; Petric, A ; Pierel, JDR ; Polletta, MDC ; Roettgering, HJA ; Rutkowski, MJ ; Smail, I ; Straughn, AN ; Strolger, L-G ; Swirbul, A ; Trussler, JAA ; Wang, L ; Welch, B ; B. Wyithe, JS ; Yun, M ; Zackrisson, E ; Zhang, J ; Zhao, X (IOP Publishing Ltd, 2023-01-01)
    Abstract We give an overview and describe the rationale, methods, and first results from NIRCam images of the JWST “Prime Extragalactic Areas for Reionization and Lensing Science” (PEARLS) project. PEARLS uses up to eight NIRCam filters to survey several prime extragalactic survey areas: two fields at the North Ecliptic Pole (NEP); seven gravitationally lensing clusters; two high redshift protoclusters; and the iconic backlit VV 191 galaxy system to map its dust attenuation. PEARLS also includes NIRISS spectra for one of the NEP fields and NIRSpec spectra of two high-redshift quasars. The main goal of PEARLS is to study the epoch of galaxy assembly, active galactic nucleus (AGN) growth, and First Light. Five fields—the JWST NEP Time-Domain Field (TDF), IRAC Dark Field, and three lensing clusters—will be observed in up to four epochs over a year. The cadence and sensitivity of the imaging data are ideally suited to find faint variable objects such as weak AGN, high-redshift supernovae, and cluster caustic transits. Both NEP fields have sightlines through our Galaxy, providing significant numbers of very faint brown dwarfs whose proper motions can be studied. Observations from the first spoke in the NEP TDF are public. This paper presents our first PEARLS observations, their NIRCam data reduction and analysis, our first object catalogs, the 0.9–4.5 μm galaxy counts and Integrated Galaxy Light. We assess the JWST sky brightness in 13 NIRCam filters, yielding our first constraints to diffuse light at 0.9–4.5 μm. PEARLS is designed to be of lasting benefit to the community.
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    A Gradual Decline of Star Formation since Cluster Infall: New Kinematic Insights into Environmental Quenching at 0.3 < z < 1.1
    Kim, KJ ; Bayliss, MB ; Noble, AG ; Khullar, G ; Cronk, E ; Roberson, J ; Ansarinejad, B ; Bleem, LE ; Floyd, B ; Grandis, S ; Mahler, G ; McDonald, MA ; Reichardt, CL ; Saro, A ; Sharon, K ; Somboonpanyakul, T ; Strazzullo, V (IOP Publishing Ltd, 2023-09-01)
    Abstract The environments where galaxies reside crucially shape their star formation histories. We investigate a large sample of 1626 cluster galaxies located within 105 galaxy clusters spanning a large range in redshift (0.26 < z < 1.13). The galaxy clusters are massive (M 500 ≳ 2 × 1014 M ⊙) and uniformly selected from the SPT and ACT Sunyaev–Zel’dovich surveys. With spectra in hand for thousands of cluster members, we use the galaxies’ position in projected phase space as a proxy for their infall times, which provides a more robust measurement of environment than quantities such as projected clustercentric radius. We find clear evidence for a gradual age increase of the galaxy’s mean stellar populations (∼0.71 ± 0.4 Gyr based on a 4000 Å break, Dn4000) with the time spent in the cluster environment. This environmental quenching effect is found regardless of galaxy luminosity (faint or bright) and redshift (low or high-z), although the exact stellar age of galaxies depends on both parameters at fixed environmental effects. Such a systematic increase of Dn4000 with infall proxy would suggest that galaxies that were accreted into hosts earlier were quenched earlier due to longer exposure to environmental effects such as ram pressure stripping and starvation. Compared to the typical dynamical timescales of 1–3 Gyr of cluster galaxies, the relatively small age increase (∼0.71 ± 0.4 Gyr) found in our sample galaxies seems to suggest that a slow environmental process such as starvation is the dominant quenching pathway. Our results provide new insights into environmental quenching effects spanning a large range in cosmic time (∼5.2 Gyr, z = 0.26–1.13) and demonstrate the power of using a kinematically derived infall time proxy.